We are investigating the formation and stability of hybrid double alphahelices; i.e. double alpha helices in which the two associated chains are different, even to the extent of being from different organisms. In particular, Clam-worm hybrid helices have been formed and the equilibrium concentration of hybrids in mixtures at various temperatures is being measured by a method involving selective cross-linking of clam-clam chains and subsequent analysis using SDS-PAGE. Worm tropomyosin has been prepared (for the first time) characterized, and shown to be suitable for similar hybridization with rabbit tropomyosin. At the same time, hydroxylapatite chromatography is being used in an attempt to find a better method of determining the relative amounts of hybrid in such solutions.